Separate from issues of safety, questions remain surrounding nanocellulose localization, detection, and migration, especially in products such as reinforced papers for food packaging. In this work, we use a straightforward method to produce fluorescent cellulose nanofibrils (CNF) of different qualities with the aim of using this material to quantify potential leaching from nanocellulose-containing papers. To do this, enzymatically pre-treated pulp was labelled with 5-([4,6-Dichlorotriazin-2-yl]amino)fluorescein hydrochloride (DTAF) in a one-pot reaction followed by extensive purification to remove unbound dye. Microfluidization was employed to generate fluorescent CNF of different qualities by varying the number of passes through the microfluidizer (1, 3 or 10 passes). The degree of DTAF labelling for the CNF was ~2 µmol DTAF/g cellulose, a value that decreased to ~1.5 µmol DTAF/g cellulose after further purification by ultrafiltration. This degree of labelling was enough to impart sensitive and quantitative fluorescence detection but not so much as to significantly alter other material properties, indicating that the fluorescent CNF is a good mimic for unmodified CNF. Fluorescence detection was used to study the CNF leaching from CNF-containing papers using cold-water and hot water-assays based on a standard assay designed for food contact papers. CNF leaching levels of ~1% were obtained, with slightly higher values in the hot water assays, and slightly lower values obtained for the finer quality CNF tested (10 passes in the microfluidizer).<br/>

Fluorescently-labelled cellulose nanofibrils for leaching detection

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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